The common loon’s mournful yodel has new significance, according to researchers who traced the impacts of environmental pollution on this denizen of northern wilderness. The 18-year study—conducted by the Wildlife Conservation Society (WCS), the BioDiversity Research Institute, and other organizations—confirms that human-generated mercury emissions degrade the health and reproductive success of loons in the Northeast.

Researchers caught and released common loons on 80 lakes in Maine, New York, New Hampshire, and other states and provinces, collecting nearly 5,500 samples of blood, feathers, and eggs to test for levels of methylmercury—the most toxic form of mercury that accumulates up the food chain.

Behavioral observations proved that loons with high levels of mercury—about 16 percent of the adult population in the study area—will spend about 14 percent less time at the nest. Unattended eggs are vulnerable to chilling and raids by minks, otters, raccoons and other predators. Loon pairs with elevated mercury levels rear 41 percent fewer fledged young than loons in lakes relatively free of mercury. The toxin also results in sluggishness, causing the birds to catch fewer fish for both themselves and their chicks.

The concentration of mercury in loons has physiological impacts as well: Afflicted loons have unevenly sized flight feathers. They expend significantly more energy than normal birds to fly, and may have trouble migrating and maintaining a breeding territory.

“This study confirms what we’ve long suspected. Mercury from human activities such as coal-burning power plants is having a significant, negative impact on the environment and the health of its most charismatic denizens, and potentially, humans,” said Nina Schoch of the WCS Adirondack Program. “Thus, it becomes even more urgent for the EPA to propose effective national regulations for mercury emissions from power plants that are based on sound science.”